A communication network is a set of geographically distributed nodes and communication links between the nodes for data transmission. The communication between nonadjacent nodes in the communication network may be realized through intermediate nodes, and this saves resources of the communication network and improves the resource utilization. Currently, various types of communication networks exist, such as synchronous digital hierarchy/synchronous optical network synchronous (SDH/SONET) networks and IP networks. Nodes in the communication network usually communicate with each other by exchanging data frames or packets over the network, and the frames or packets are defined by a specific protocol such as Transmission Control Protocol/Internet Protocol (TCP/IP). Herein, the protocol means a set of rules which are similar to TCP/IP and define inter-node interaction.
When the communication network becomes huge, management and maintenance will be difficult. Therefore, to facilitate management, the communication network is usually divided into multiple routing domains or autonomous systems (ASs). Generally, in the network inside an AS, conventional intra-domain routers that execute intra-domain routing protocols are coupled together and managed by common powers. For the purpose of improving route flexibility, an AS is usually divided into multiple areas. Generally speaking, a domain is any collection of network elements within a common sphere of address management or path computation responsibility. Examples of domains include areas, AS, and multiple ASs. For ease of description, routing domains, ASs and areas are collectively referred to as domains herein. The specific meaning of a domain depends on its context. When nodes are added for data exchange, inter-domain routers that execute inter-domain routing protocols are adopted to interconnect the nodes in different domains. Such inter-domain routers are also referred to as border routers.
An example of inter-domain routing protocol is the Border Gateway Protocol (BGP) version 4. The BGP implements inter-domain routing by exchanging routes and reachable information between adjacent inter-domain routers in the system. The BGP usually adopts a reliable transmission protocol such as TCP to establish connections and sessions. An example of intra-domain routing protocol, or Interior Gateway Protocol (IGP), is the Open Shortest Path First (OSPF) routing protocol. The OSPF protocol is based on a link state technology, and therefore is also a link state routing protocol. The link state routing protocol defines a mode of exchanging and handling intra-domain routing information and network topology information, for example, in the OSPF protocol, the information is exchanged through Link State Advisement (LSA).
The emergence and development of Multi-Protocol Label Switching (MPLS) technology meets the new requirements for data network development, such as guaranteed available bandwidth and fast restoration. The MPLS technology allows the establishing of end-to-end tunnels in an IP/MPLS network having Label Switched Routers (LSRs). Such tunnels are generally referred to as Label Switch Paths (LSPs). LSP establishment involves the computation of a path of an LSR in the network, which is generally called route computation.
The MPLS technology has also been introduced to the field of optical transport networks, based on which an Automatically Switched Optical Network (ASON) has been developed. Unlike the conventional optical transport network that provides network connection services through manual or semi-automatic configuration, the ASON provides network connection services through automatic establishment of the control plane. The ASON may be divided into a transport plane that bears network services, a management plane that implements management functions, and a control plane that runs a control protocol.
The technology used by the control plane of the ASON is called Generalized Multi-Protocol Label Switching (GMPLS), which extends the MPLS technology to include the Link Management Protocol (LMP), routing protocol and signaling protocol. The LMP obtains the connection types supported by the link and the number of resources through packet exchange based on discovery of neighboring relations. Such information is referred to as Traffic Engineering (TE) information, and a link that includes TE information is referred to as a TE link. Inside a domain, the local link TE information is advertised to other nodes in the domain through a routing protocol such as OSPF-TE. Based on the information, when the network management system or a user requests the network to establish a network connection, the ingress node of this connection can perform path computation to obtain the link sequence of the connection, and, through a signaling protocol such as the Resource Reservation Protocol-Traffic Engineering (RSVP-TE), send a request to the nodes on the path for resource allocation and establish a cross connection, thereby establishing an end-to-end connection.
For both IP/MPLS and optical transport networks, the division of domains is a concern. Especially, when a network with TE management capabilities is divided into multiple domains, each node only stores the TE information of the local domain and the reachable information of other domains, which reduces the impact of the change in the network topology on new service deployment and congestion recovery, and enhances the network scalability. However, as each node only stores the TE information of the local domain and the reachable information of other domains but does not know the complete TE information of other domains, it becomes a problem to be solved how to compute an end-to-end path that meets all the requirements on bandwidth, switching capability, route separation, protection, and user policies in the case of multiple domains.
To solve the route computation or path computation (hereinafter collectively referred to as route computation for ease of description) in the case of multiple domains, the Domain-Domain Routing Protocol (DDRP) adopts a hierarchical network model, in which, a lower-level domain is represented by an agent node in the upper level. The agent node can advertise abstract topologies, inter-domain links, and reachable addresses that represent the domain. Thus, a hierarchical network takes shape. When an end-to-end path that crosses multiple domains is computed, the strict route in the domain of the requesting node and the subsequent loose route of the border node are computed first. When signaling flows to the border of an intermediate domain, the strict route in this intermediate domain is computed through domain border computation and the like. Such operations are continuously performed until the signaling reaches the domain of the destination node.
As shown in FIG. 1, in another technology that solves the route computation in the case of multiple domains, that is, PCE technology, each PCE stores all TE information of the domain that the PCE serves (for ease of description, the TE information includes network topology information herein). A node requesting route computation is called a Path Computation Client (PCC). The PCC sends a request that includes route computation parameters to a PCE, and the PCE performs a route computation according to the Traffic Engineering Database (TED) stored therein and feeds back the result to the PCC. The PCE may store TE information of one or more domains. When a route crossing multiple domains is computed, if the route is beyond the service area of the local PCE, the PCE will use the Path Computation Element Communication Protocol (PCECP) to collaborate with other related PCEs so as to compute the final route.
During the implementation of the present invention, the inventor finds that, the prior art has at least the following problems.
According to the solution provided by a first conventional technology, route computation is a serial process. At the head node, only the ingress and egress information of some domains that the path passes through is available. Because the real TE information in related domains is unavailable, it cannot be determined whether route computation can succeed from the ingress to egress until signaling flows to the corresponding domain border and triggers domain border computation. Thus, it may frequently occur that signaling discovers during the transmission that no route is available or no route satisfies related constraints. As a result, route establishment is rolled back for multiple times, and the previously established cross connection has to be removed for re-establishment. In addition, for this technical solution, it is difficult to compute end-to-end diverse routes (different paths with the same source and destination).
The second conventional technology adopts a flat single-level model, that is to say, all PCEs are equally important. When the network is complex or large, it is difficult to manage the PCEs. In addition, as hierarchical abstraction is not applied to the network, cross-domain route computation entirely relies on the exchange of TE information of different domains between different PCEs. When a service passes through many domains, communication between related PCEs will be too frequent and the amount of information exchanged will be huge, which reduces the efficiency and reliability of route computation.